Manufacture of artificial silk



Patented Apr. 25, 1939 UNITED STATES 2,155,934 PATENT OFFICE 2,155,934 MANUFACTURE or ARTIFICIAL SILK V Otto Eisenhut, Heidelberg, Hanns Rein, Hamburg vor der Hohe, and Erich Kaupp, Ludwigshafenon-the-Rhine, Germany, assignors to I. G. Farbenindustrie Aktiengesellschaft, Frankfort-onthe-Main, Germany No Drawing. ApplicationJune 2, 1936, Serial No.

4 Claims.

Another object is to produce artificial silk fromviscose which has the character of artificial silk produced according to the copper ammonia process. Still another object are the threads produced according to our new process which have the character of copper, ammonia silk though spun from viscose. Further objects will be seen from the detailed specification following hereafter.

When it is attempted to make a thread from normally ripened or unripened viscose with the use of water as the-first precipitating bath, there is diificulty in obtaining a thread having the properties necessary for good artificial silk. This difficulty is encountered in the entire normal range of ripeness of the viscose, that is to say from high salt points to the lowest usual salt point. r I

We have found that viscose can be spun without troubles into water as a first' precipitating bath, for instance, while using a spinning funnel, if the viscose is ripened below the usual ripeness corresponding with an ammonium chloride number of '7 to 6 (Hottenroth number).

At normal temperature, a few days elapse between the time when the viscose has the lowest stage of ripeness (which can be determined by the usual measuring methods) and the time when the viscose spontaneously c'oagulates; the state of ripeness of the viscose solution, which increases during this lapse of time, can be followed exactly and fixed chronologically. The spontaneous coagulation point generally occurs, at a ripening temperatureof 20 C., at about 7 days after a ripeness below the Hottenroth number of 7 has been attained.

There is no objection to the acceleration of the degradation of the 'xanthate molecule by raising the temperature.

When spinning is conducted in the interval of time between the ammonium chloride number 7 to 6 and the spontaneous coagulation (which naturally must be avoided) the viscose is degraded to such an extent that it may be coagulated by water alone or by unusually strongly diluted electrolyte solutions. Such solutions of electrolytes are those which have a precipitating power at most equal to that of an aqueous solution of 1% of sodium sulfate and 0.2% of sulfuric acid. A spinning bath having a precipitating power at most equal to that of an aqueous solution of 1% of sodium sulfate and 0.2% of sul- In Germany October 10, 1933 furic acid is a spinning bath having a pH-value of 1.0 to 11 and an osmotic pressure corresponding at most with that of an aqueous solution of 1% of sodium sulfate and 0.2% of sulfuric acid. The concentration of the electrolyte in the precipitating bath obviously varies with the spinning conditions and the particular viscose to be spun. The most suitable composition will easily be found by a few comparative experiments. It mayalsobe advantageous to use a solution which contains only salt or only acid as a precipitating bath, however, as a rule a solution containing salt and acid is preferred. The coagulation may be carried out either in a spinning funnel or in an open bath. The coagulation can also be completed subsequently by means of a strongly diluted acid or salt solution or both. The consumption of water is slight; it amounts approximately to M -1J0 cbm. of cold water per kilo of silk.

Any titer may be spun by this process, to which any cellulose can be subjected, but for which the use'of little degraded cellulose is preferred. The use of little degraded cellulose involves the advantage that the thread obtained has a high viscosity and is sparingly soluble in solutions of alkali. The speed of spinning may amount to ms. and more per minute; in particular, when the temperature of the water is raised the speed draft can be increased. The same result can be obtained when spinning with cold water if unusually long precipitating baths (funnels) are used. For instance, when spinning a thread having a single titer of 3 deniers andja total titer of 300 deniers the length of the spinning funnel is about 50 to 60 centimeters. In general the length of the spinning funnel must be greater when spinning a higher titer and vice versa.

The effect of the extraordinarily unstable con dition of the viscose molecule in the vicinity of the spontaneous coagulation point, and the merely slight chemical attack necessary for full decomposition of the much degraded xanthate molecule is that the thread material separated in the precipitation of the cellulose is very similar to the material obtained by the copper silk process. The precipitation is preferably carried out in a spinning funnel. The thread is soft to the touch, the cross-sections are round, that is to say similar to those of copper silk, the tensile strength varies between 140 and 200 grams per deniers, and the extension between 12 and 20 per cent and more. The capacity of the material for being dyed is at least as strongly substantive as that of normal copper silk. Thus, the capacity of copper ammonia silk and of the material according to this invention for being dyed with Diamlnpure blue FF (sf. Schultz Farbstofitabellen, 6th edition (C) 424) without the addition of salt, is

the same, while the usual viscose silk is hardly dyed by this dye without the addition of salt. The material according to this invention shows the same structure as copper ammonia silk when investigated by X-rays. The material is softto the touch, is warm and wooly, that is to say is similar to copper silk in this respect also. The material according to this invention differs from copper ammonia silk in that it contains no traces of copper. That the artificial threads made according to this invention are produced according to the viscose process is evident from the fact that they still contain in the finished condition traces of sulfur which can be detected by a sufficiently sensitive method for detecting sulfur.

. The following examples illustrate the invention:

Example 1.Viscose containing 7.5 per cent of cellulose, 8 per cent of NaOI-I and which has been sulfidized with 31.5 per cent of CS2 calculated on the quantity of cellulose from which is started, is stored after having attained the normal ammonium chloride number of 6, for a further three days at 20 C. it is then passed under a pressure of 8.5 atmospheres, through a spinning head having 92 holes (individual hole diameter about 0.8 mm.) into a spinning funnel,

through which flows a slow stream of water of 20 C. A normal coagulation occurs. The thread formed, after leaving the funnel, is passed over a roller or a rod and conducted through a trough through which a dilute acid or a salt solution or a solution of acid and salt flows. There may be used, for example, a sulfuric acid of 3.5 per cent strength in which 6 per cent of sodium sulfate is dissolved. The solution can be used in circulation while keeping its composition and concentration constant. The reeling occurs at a distance of to 1 m. from this trough. The speed of draft is 80 m. per minute. The spun material (titer 140) is then after-treated in normal manner. The thread is strongly substantive in dyeing, is of round cross-section, and is soft to the touch.

Example 2.Viscose prepared as described in Example 1, is coagulated in a spinning funnel into an aqueous solution containing 0.5 per cent of NazSO; and 0.025 per cent of H2SO4. The coagulated thread is guided over a roller or a rod and passe-d through a bath of per cent of sulfuric acid and 3 per cent sodium sulfate. The supply of the spinning liquid and the other spinning conditions are so selected that a thread with a total titer of 120 deniers and a single titer of 1.3 deniers is formed. The resulting thread of which the filaments are well closed and have a round cross-section, has a tensile strength in the dry state of 203 grams per 100 deniers and an extensibility of 14.6 per cent. It possesses the dyeing properties of copper ammonia silk.

Example 3.Viscose containing 7 .5 per cent of cellulose and 7 per cent of NaOH which was stored for three days at C. after having reached the normal Hottenroth degree of 6, is pressed at 8.5 atmospheres through a spinning head with 90 openings of 0.8 mm. diameter each into a spinning funnel through which flows slowly a current of water of 14 C. The rate of viscose supplied per minute is regulated so that at a speed of draft of 40 meters per minute there is produced a single titer of 0.47 denier. After leaving the funnel the thread is guided through a channel. Through this channel flows sulfuric acid of 10 per cent strength containing 3 per cent of sodium sulfate. The tensile strength of the thread which has the dyeing properties of copper ammonia silk and the filaments of which are well closed. amounts to 212 grams per 100 deniers and the extensibility to 11.3 per cent.

The spinning temperature depends upon the single titer which is spun and the degree of ripeness of the viscose. The higher the single titer the higher is, the spinning temperature the remaining conditions of operation being the same. For instance, when using permutite water having a carbonate hardness of 1.5 and spinning a single titer of 3 deniers with a viscose having a degree of ripeness of 1.5 through a spinning funnel of 60 centimeters length at a speed of draft of 60 meters per minute, a spinning temperature of C. hase been found to be suitable. These statements are however not intended to limit the invention, but the most suitable spinning conditions in each particular case will be found by a few comparative experiments.

What we claim is:

1. A process of manufacturing artificial silk from viscose which comprises squirting viscose having a degree of ripeness below 7 Hottenroth through the openings of a spinning nozzle into a precipitating bath having a pH value of from 1 to 11 and an osmotic pressure corresponding at most with that of an aqueous solution of 1 per cent of sodium sulfate and 0.2 per cent of sulfuric acid.

2. A process of manufacturing artificial silk from viscose which comprises squirting viscose having a degree of ripeness below 7 Hottenroth through the openings of a spinning nozzle into a spinning funnel and passing through said spinning funnel a precipitating bath having a pH value of from 1 to 11 and an osmotic pressure corresponding at most with that of an aqueous solution of 1 per cent of sodium sulfate and 0.2 per cent of sulfuric acid.

3. A process of manufacturing artificial silk from viscose which comprises squirting viscose having a degree of ripeness below 7 Hottenroth through the openings of a spinning nozzle into a precipitating bath having a pH value of from 1 to 11 and an osmotic pressure corresponding at most with that of an aqueous solution of 1 per cent of sodium sulfate and. 0.2 per cent of sulfuric acid, and passing the formed threads through a hardening bath.

4. A process of manufacturing artificial silk from viscose which comprises squirting viscose containing 7.5 per cent of cellulose and 8 per cent of NaOH, and which after having reached the Hottenroth degree of 6 has been stored for three days at 20 0., through a spinning head having openings of 0.8 mm. diameter each, into a spinning funnel through which is passed a solution containing 0.5 per cent of sodium sulfate and 0.025 per cent of sulfuric acid, and hardening the formed threads in a bath of 10 per cent of sulfuric acid and 3 per cent of sodium sulfate.

OTTO EISENHUT HANNS REIN. ERICH KAUPP. 

